Naruto: Eightfold Dragon Transformation, Saving the Third Hokage from the Start

A Naruto fanfic: invincible protagonist, System, saving the day from the start, and a carefully constructed setting. After transmigrating into the world of Hokage, he gains the power of the dragon and becomes Genma, the Azure Dragon of Konoha, a legendary ninja of the Second Great Ninja War. After more than twenty years wandering abroad, he finally returns. The Chunin Ninja Exams are underway, and Konoha is on the brink of collapse. As the Third Hokage Hiruzen Sarutobi prepares to use the Reaper Death Seal, a large hand lands on his shoulder just as he is about to form the hand signs. “Old man, it's been years. I come back and find you ready to risk your life. What an extravagant welcome.”